When treating diabetes, it is important to control the patient's blood sugar level within the normal range, and so it is important that the patient has a control on his own blood sugar level. Especially for insulin-dependent patients, it is essential to check their blood sugar level regularly in their daily life in order to maintain the blood sugar level within the normal range. Since it is inconvenient to make frequent visit to a medical institute for the blood sugar measurement, portable blood sugar level testers are used so that the blood sugar level can be measured without the burden of visiting medical institutes.
An example of the portable blood sugar level tester is shown in FIG. 12 of the present application. This blood sugar level tester 8 uses an attachment 7. The attachment 7 includes a main body 70, which includes, integrally therewith, a lancing member 71 and a biosensor 72. The main body 70 has a housing space 73 for housing the lancing member 71. The housing space 73 has an opening 74, which is closed by the biosensor 72. The biosensor 72 provides an enzyme reaction field, and includes a layer of reagent containing an enzyme and an electron transfer material. The biosensor 72 is formed with a through hole for insertion of a lancing member 75 of the lancing member 71.
If the blood has to be sampled from a region which does not bleed easily, the blood sugar level tester 8 can be used to massage the target area Sk for improved blood flow, or the blood sugar level tester 8 can be used to press the target area Sk. Instead, the area may be sucked to cause blood congestion, or treated in different ways to promote bleeding from the target area Sk. In these actions, the target area Sk tends to bulge as shown in an imaginary line in the drawing, yet if the biosensor 72 is fixed on, the target area Sk is pressed onto the biosensor 72, and thus the target area Sk cannot bulge, leading to insufficient bleeding. If bleeding is insufficient, the biosensor cannot be supplied with a sufficient amount of blood necessary for the blood sugar level measurement, which can lead to an unacceptably large error in the measurement, or a process error in measuring steps. On the contrary, some parts of the human body may not bulge very much, and bulging of the skin varies from person to person. Under these conditions, there can be a case where the biosensor does not touch the skin at the time of lancing.
According to the attachment 7, the lancing needle 75 is exposed whether or not the biosensor 72 is integrated therewith. However, in view of sanitation on the lancing needle 75, the lancing needle 75 needs to be sterilized, and in order to prevent contamination after the sterilization, the lancing needle 75 must be sterilized as sealed in a space, and the sealing must be maintained till the time of use. Now, in order for the lancing needle 75 to be kept appropriately sterilized, the attachment 7 must be sealed with an aluminum laminate seal for example while the lancing member 71 and the biosensor 72 must be integrated into the main body 70. This is not possible for the attachment 7 in FIG. 12. Specifically, the lancing needle 75 cannot be sterilized separately from the biosensor 72 or from the enzyme contained in the biosensor 72.
The sterilization of the lancing needle 75 is made with gamma rays for example. Existence of an enzyme during the sterilization process, therefore, means that the enzyme will be destroyed or enzyme activity will be reduced. If such happens, a longer time will be required for the measurement, or the measured concentration can be lower than real, and in fact it becomes impossible to make appropriate measurement.
There is another problem: If the electron transfer material is provided by potassium ferricyanide, the gamma ray radiation reduces the potassium ferricyanide to potassium ferrocyanide. This is problematic if an amperometric method is used in the measurement of oxidation current, because part of the electron transfer material in the chemically reduced state is derived by the gamma ray radiation at the time of sterilization while the rest being derived from the enzyme reaction. Accordingly, when the electron transfer material in the chemically reduced state is oxidized by a voltage, a measured value of the oxidation current will be greater, which will give a concentration measurement higher than the real value, i.e. measuring accuracy will be low.